Injection molding processes and apparati typically involve heating materials which are solid at room temperature to elevated temperatures where the solid materials are converted to a fluid capable of flowing readily through tubes, barrels, bores and channels of various shapes and sizes that direct the fluid to the cavity of a mold where the fluid is cooled and formed into a solid part. Heating of the fluid flow channels in injection molding machine apparati and processes has been attempted in a variety of configurations and devices that have been designed to achieve the most efficient contact possible between a source of heat and the paths/channels through which the fluid is routed. In order to maintain injected fluid at an elevated temperature, various heating devices such as wires, coils, tubes and the like are placed in direct contact/engagement with the housings of the apparatus. Such heating devices/methods rely on conduction of heat throughout the body or matrix of the components to travel to the walls of the fluid flow channels.
The present invention relates to heating of a fluid flow channel in an injection molding apparatus, and more particularly to an apparatus and method for ensuring intimate contact between the heating device and the body of the apparatus or system component that is sought to be heated to an elevated temperature.
In accordance with the invention therefore there is provided in one embodiment, a heater assembly for mounting around a fluid flow channel in an injection molding apparatus, the heater assembly comprising: an inner tube comprising a first heat conductive material having a first coefficient of thermal expansion, the inner tube having a selected longitudinal length, an inner surface, an outer surface; a first ring having an inner surface engaged around the outer surface of the inner tube along short selected length of the longitudinal length of the inner tube, the first ring comprising a second material having a second coefficient of thermal expansion that is less than the first coefficient of thermal expansion; and, a heater mechanism that heats the inner tube to a selected elevated temperature.
The heater assembly may include an outer tube receiving and mounted around the outer surface of the inner tube, the first ring mounting the outer tube in a fixed position around the outer surface of the inner tube, the outer tube being mounted such that an inner surface of the outer tube is spaced a distance from the outer surface of the inner tube. The heater mechanism is typically mounted within the space between the inner ring and the outer ring.
The assembly preferably includes a second ring having an inner surface engaged around the outer surface of the inner tube along a second short selected length of the longitudinal length of the inner tube, the second ring comprising a third material having a third coefficient of thermal expansion that is less than the first coefficient of thermal expansion. The second ring mounts the outer tube in the fixed position around the outer surface of the inner tube in cooperation with the first ring.
The second material and the third material typically have the same or substantially the same coefficient of thermal expansion.
The short selected length typically extends from a first terminal end of the inner tube, the first ring being mounted at and around the first terminal end of the inner tube. The second short selected length typically extends from a second terminal end of the inner tube, the second ring being mounted at and around the second terminal end of the inner tube.
The inner tube and the first ring expand radially upon heating to select elevated temperatures, the second material of the first ring being selected such that the first ring expands less radially than the inner tube expands radially upon said heating, the first ring restricting radial expansion upon said heating. The inner tube and the second ring expand radially upon heating to select elevated temperatures, the third material of the second ring being selected such that the second ring expands less radially than the inner tube expands radially upon said heating, the second ring restricting radial expansion upon said heating.
The inner tube preferably includes a slot extending the longitudinal length of the inner tube.
The outer tube receives and is mounted around the outer surface of the inner tube by the first and second rings such that an inner surface of the outer tube is spaced a selected distance from the inner surface of the inner tube, an enclosed space being formed between the first and second rings and between the inner surface of the outer ring and the outer surface of the inner ring.
The heater mechanism is preferably mounted in the enclosed space in engagement with the outer surface of the inner tube and being spaced a distance from the inner surface of the outer tube.
The heater mechanism typically comprises a metal material connected to a source of electrical energy for controllably heating the metal material by controlled application of electrical energy to the metal material.
Further in accordance with the invention there is provided a heater assembly for mounting around a fluid flow channel in an injection molding apparatus, the heater assembly comprising: a tube comprising a first heat conductive material, the inner tube having a selected longitudinal length, an inner surface and an outer surface; a first ring having an inner surface engaged around the outer surface of the inner tube along short selected length of the longitudinal length of the inner tube; and a second ring having an inner surface engaged around the outer surface of the inner tube along second short selected length of the longitudinal length of the inner tube; and, a heater mechanism mounted around and in engagement with the outer surface of the inner tube.